Photolithography has hitherto been used in the manufacture of flat panel displays (FPDs) such as liquid crystal displays, semiconductor devices, charge-coupled devices (CCDs) or color filters. For example, in a photolithographic process for producing integrated circuits, a positive- or negative-working resist is cast on a substrate, then baked to remove the solvent, thereafter exposed to radiation such as UV light, far UV light, electron beams or X-rays, and finally developed to form a resist pattern.
In accordance with recent technological progress, semiconductor devices have been required to be highly integrated and hence miniaturization of resist patterns has been regarded as a problem to solve. Meanwhile, it has been also desired to provide a method capable of producing semiconductor devices at low cost and in high productivity. In view of this background, various photolithographic processes have been studied and brought into practice. Further, according to that, various researches have been made on new materials employed in those lithographic processes.
Hitherto, silicon oxide films have been generally adopted as masks of photoresist. The silicon oxide films can be relatively easily formed by casting and then firing compositions containing, for example, polysilazane, polysiloxane or the like, and therefore have been used in a great many processes. However, even the silicon oxide films cannot always fulfill their functions, and accordingly there is a case where the masks need to be made of new materials in place of silicon oxide. As one of those new materials, tungsten oxide is proposed.
Tungsten oxide films have a relatively low volume shrinkage ratio, and accordingly hardly suffer from defects such as voids. Further, they also have another advantage of being easily removed away by washing with water or the like. Accordingly, the tungsten oxide films often exhibit properties more advantageous than the silicon oxide ones. However, it has been difficult to produce tungsten oxide films by casting compositions in the same manner as the silicon oxide films, and hence they have been generally produced according to vapor deposition methods. Because of that, there is a problem in that the productivity thereof cannot be enhanced.
Although there is a known method to form a tungsten oxide film from an aqueous solution (e.g., Patent document 1), there is not any known method in which both coatability and film-formability are satisfying enough to apply to lithographic processes for producing semiconductor devices.